The shooter who claimed the lives of four people in an attack on the Brussels Jewish Museum late last month had been tracked by French authorities for a year, Israeli media reported Sunday, as European governments vowed to bolster efforts to stymie jihadis returning from Syria.

The suspected shooter, Mehdi Nemmouche, was arrested in France on Friday, having reportedly claimed responsibility for the shooting on a tape.

French officials said Nemmouche spent a year in Syria, and Paris had tracked him since he returned to Europe via Malaysia in 2013, Israel’s Channel 2 news reported Sunday night.

French Interior Minister Bernard Cazaneuve said that Nemmouche had become radicalized in prison, and called for better international coordination on the threat of terrorists returning from the fighting in Syria.

His Belgian counterpart, Joelle Milquet, called the returnees “a generalized problem for all of Europe,” at a joint press conference.

Interior ministers from around the European Union are expected to focus on better ways to stem Syria-related violence when they meet in Brussels on Thursday.

Nemmouche filmed a short video after the shootings in which he claimed responsibility for the May 24 attack, Paris prosecutor Francois Molins said Sunday in a press conference. The film also showed the weapons Nemmouche used in the assault, according to AFP.

In the film, the suspect was wrapped up in a white sheet scrawled with the name of the Islamic State of Iraq and the Levant, an al-Qaeda-linked extremist group fighting in Syria, Molins said. He said the suspect had spent about a year in Syria.

Nemmouche, a 29-year-old from the northern French town of Roubaix, was arrested Friday in Marseille in possession of a gun and an AK-47 assault rifle of the sort used in the attack.

He is suspected of having jihadist links.

In Brussels, Belgian federal prosecutor Frederic Van Leeuw said the suspect had tried to film the killings on May 24, but his camera failed. The video found after his arrest shows his weapons and clothes, and includes his voice claiming responsibility for the attack, Van Leeuw said.

Belgian police carried out raids relating to the case in the Courtrai region of Belgium on Sunday morning, where the suspect is believed to have spent time, and were questioning two people there, Van Leeuw said.

“The new elements in this investigation draw attention once more to the problem of the ‘returnees’ —in other words the people going to Syria to participate in combat and return afterward to our country,” he said. “All European countries are confronted at this moment with this problem.”

The shooting by the lone gunman in the Brussels Jewish Museum killed three people outright — an Israeli couple and a French woman — while the fourth victim, a 24-year-old Belgian man, was left clinically dead.

Authorities had released chilling security camera footage of the gunman wearing a cap and sunglasses, walking into the museum, removing an automatic rifle from a bag and shooting through a door before making an exit.

Belgian media had reported that the assailant used a camera to film his attack in the same way as Mohammed Merah, the Frenchman who shot and killed Jewish schoolchildren in Toulouse two years ago.

This videograb released on May 25, 2014, by the Belgian federal police on demand of Brussels’ king’s prosecutor, shows the suspect of the killings in the Jewish Museum on May 24, 2014 in Brussels. (photo credit: AFP photo/Belga/Belgian Federal Police/handout)

He is being questioned by the DGSI, France’s internal intelligence agency, who can hold him for up to 96 hours, until Tuesday, or 144 hours, to Thursday, if investigators invoke an imminent terrorist threat.

Sources close to the investigation told AFP that Nemmouche remained silent during the first 24 hours of interrogation.

The attack was the first such incident in more than 30 years in Belgium and has revived fears of a return of violent anti-Semitism to Europe.

The profile of Nemmouche also stands to revive a row in France over the monitoring of those who leave to country to fight in Syria.

France unveiled plans in April to try and stop the increasing numbers of young French Muslims heading to fight in Syria’s civil war and becoming radicalized before returning home.

President Francois Hollande said Sunday that the suspect was “arrested as soon as he set foot in France.”

“The government is mobilized to track down jihadists and prevent them from causing more harm,” he said, adding that the action plan to fight them will “be strengthened in the coming months.”

According to the latest figures, some 780 people have left France to fight with jihadists in Syria.

(This story was updated to delete an inaccurate report that the Belgian and French interior ministers attributed the killings to anti-Semitism.)